1. Field of the Invention
The invention generally relates to an electromechanical program timer, and in particular relates to a program timer having at least a section with reduced timing speed different from a major timing speed.
2. Related Art
There have been so many home appliances, such as air conditioners, televisions, dishwashers and clothes washing machines, which help people comfortable and easy in their daily lives. No wonder how hard it would be for us if all these appliances were gone.
Many home appliances have timer functions that control the appliances on/off or other functions according to user""s or the appliance default settings. In a washer, for example, a dial knob is provided for user to choose programs of automatic washing and drying. The dial usually is an electromechanical program timer having a cam drum or a cam disk driven by a gear reduction motor for activating several electrical contact portions (blade switches) in predetermined timing defined by tracks on the cam unit. Correspondent actuators, such as water inlet solenoid, heater, spinning motor and draining motor, that connected to the contact switches are then controlled on and off by each track of the cam unit. There is a kind of driving mechanism of the cam unit that uses an eccentric rotor for oscillating a drive pawl and pushing the cam unit with step-by-step increments instead of using reduction gears.
Whatever a driving mechanism is used, the cam unit moves in a predetermined timing speed as the driving motor runs in a specific speed. When a serial control program is made on the cam unit, the rotational cycling angle of the cam wheel (equal or less than 360 angular degree of a revolution) is shared by the whole program timing. If the program is complicated and some control tracks have relatively small activating time periods, then the resolution, precision and endurance of tracks on the cam unit are hard to be achieved due to mechanical restrictions. For example, if a serial program lasts 3 hours (180 minutes), then a half-minute on/off cam shares only 1 angular degree for forming a ramp, peak and valley on the track to activate the contact switch follower. The small peak portion is weak and easy to be deformed. Therefore, it is often desired to include more programs or longer timing intervals on a cam unit while providing higher timing resolution for some small timing intervals.
An ideal solution of the need is to provide a two-speed or multiple-speed timer that during a longer timing section, a reduced timing speed mechanism works; while at the rest, a normal timing speed mechanism functions.
In a dishwasher program timer, for example, it is often desired to set up a dishwasher but delay the running of the program cycle for a number of hours. Some attempts in the past to provide a program timer with a delayed start feature have utilized a second motor to time the delay period. Other attempts have utilized a complex arrangement driven by the timer motor to prevent the main program from becoming effective during the delay period.
U.S. Pat. No. 4,649,239 discloses a program timer having a timing cam member including a delay ratchet wheel having a pin which engages an abutment inside the cam member at one relative position of the delay ratchet to the cam member. The cam member ratchet ring has a gap at the desired delay position so that when the delay ratchet wheel is set to a desired delay, and the drive pawl is at the delay position, the drive pawl extends into the gap to only move the delay ratchet wheel until the pin engages the cam member. The cam member is then advanced along with the delay ratchet wheel until such time as the gap in the cam member ratchet ring has advanced past the drive pawl. From then on, the regular cam member advance takes over. The delay arrangement of the program timer includes additional delay ratchet wheel with at least a dead zone, resilient tabs, a shoulder and a pin. The cam member ratchet ring is also formed with gaps of omitted teeth. The root radii of the ratchet teeth are no greater than the minimum root radius of the teeth of the ratchet ring. When a delayed start is in effect, the drive pawl extends into the gap of the ratchet ring to engage the ratchet teeth of the ratchet wheel. Accordingly, the ratchet wheel is advanced. The drive pawl continues to advance only the ratchet wheel until the ratchet wheel is in such relative angular position with respect to the cam member that the pin contacts the abutment. The arrangement and construction of the delay timer is rather complicated that requires an additional delay ratchet wheel and specific engagement mechanisms.
These prior attempts all have certain drawbacks such as requiring a separate motor or complicated mechanisms.
It is an object of the present invention to provide a program timer having at least a section with reduced timing speed different from a major timing speed.
It is a further object of the present invention to provide a program timer utilizing a simple mechanism for both the reduced timing speed and the major timing speed.
An electromechanical program timer according to the invention includes a driving motor, a driving shaft, a cam disk with a main driven gear and a driven ratchet, and a pushing pawl. The driving motor rotationally drives the driving shaft through a first gear formed on the driving shaft. A second gear and an eccentric shaft are formed on the driving shaft for driving the cam disk through the main driven gear and via the pushing pawl to the driven ratchet respectively. The main driven gear includes at least a missing gear portion where the second gear is free from driving the main driven gear, and the pushing pawl and the driven ratchet take place. The driving shaft engages and rotates the cam disk through the main driven gear in a major timing speed. While at the missing gear portion, the eccentric shaft oscillates the pushing pawl and drives the cam disk through the driven ratchet in a reduced timing speed. The eccentric shaft oscillates the pushing pawl once per revolution of the driving shaft so as to provide the cam disk with the reduced timing speed.